#2 Daily Problems -FirstNotRepeatingCharacter

As I already mention in previous post, I have planned to do solve one problem per day.

Problem:

• For s = "abacabad", the output should be
  firstNotRepeatingCharacter(s) = 'c'.
• There are 2 non-repeating characters in the string: 'c' and 'd'. Return c since it appears in the string first.
• For s = "abacabaabacaba", the output should be
  firstNotRepeatingCharacter(s) = '_'.
• There are no characters in this string that do not repeat.

Input/Output

• [input] string s
• A string that contains only lowercase English letters.
• Guaranteed constraints:
  1 ≤ s.length ≤ 105.
• The first non-repeating character in s, or '_' if there are no characters that do not repeat.

My Solution:

char firstNotRepeatingCharacter(String s) {
HashSet<Character> hS=new HashSet<>();
String tS=s;
for (int i=0;i<s.length();i++){
if(!hS.contains(s.charAt(i)))
hS.add(s.charAt(i));
else
tS= tS.replace(""+s.charAt(i),"");
}
if (tS.length()>0)
return tS.charAt(0);
else
return '_';
}

Again hi guys, please just see my solution and help me to improve this if you have any suggestion for me